1. Field of the Invention
The present invention relates to a polishing cloth to be used for chemical mechanical polishing, and a chemical mechanical polishing apparatus provided with said polishing cloth.
2. Description of Related Art
In a semiconductor device production process, there are instances where a CMP (chemical mechanical polishing) processing is conducted for flattening the wafer surface.
FIG. 6 illustrates the schematic arrangement of a CMP processing apparatus of first prior art. The CMP processing apparatus comprises: a wafer head 1 which is arranged to be rotationally driven around the axis of rotation along the perpendicular direction, while suctioning and holding a wafer W with its bottom up; a polishing board 2 disposed opposite to the wafer W; and a nozzle 3 for supplying a polishing agent to the polishing board 2. The polishing board 2 comprises (i) a surface plate or platen 5 substantially in the form of a circle, in a plan elevation, of which diameter is greater than that of the wafer W, and (ii) a polishing cloth 4 fixed to the top of this platen 5. The polishing board 2 is arranged to be swung as if a circular locus is drawn along a horizontal plane.
According to the arrangement above-mentioned, the wafer W main face (which is opposite to the polishing board 2) can be polished in the following manner. That is, a load is downwardly applied to the wafer head 1 to push the wafer W against the polishing cloth 4, the wafer head 1 is rotationally driven, the polishing board 2 is swingingly driven and the polishing agent is supplied to the top of the polishing cloth 4 from the nozzle 3.
The polishing agent is composed of a slurry containing, in the form of a mixture, polishing particles such as alumina for physical polishing, and a chemical solution for chemical polishing. The polishing cloth 4 is made of foamed polyurethane for example, and is provided in the surface thereof with a number of grooves 6 in a grid pattern. Provision is made such that the polishing agent is introduced through these grooves 6 to the whole area of the polishing cloth 4.
FIG. 7 is a perspective view illustrating the arrangement of a polishing board 2A used in a second prior art. This polishing board 2A comprises a platen 5 and a polishing cloth 7 fixed to the top thereof. The polishing cloth 7 has a circular flat plate portion 7A and a number of column-like projections 7B projecting from the surface of flat plate portion 7A. In FIG. 7, the column-like projections 7B are illustrated in an exaggerated manner. In fact, the fine column-like projections 7B are arranged with high density to obtain a good polishing rate.
Alumina particles are dispersed and embedded in the column-like projections 7B. Accordingly, a physical polishing is achieved by rubbing a wafer, as coming in contact, with the tops of the column-like projections 7B. Therefore, in the second prior art, only a chemical solution for chemical polishing is supplied onto the polishing cloth 7.
FIG. 8 is a section view illustrating how the CMP processing of the second prior art in FIG. 7 is executed. The wafer W held by the underside of the wafer head 1, is pushed against the polishing cloth 7 and comes in sliding contact with the tops of the column-like projections 7B. A chemical solution 9 supplied onto the top of the polishing cloth 7 passes among the column-like projections 7B disposed with high density and is supplied to respective parts of the polishing cloth 7. However, the chemical solution 9 cannot easily enter into that portion of the polishing cloth 7 against which the wafer W is pushed by the wafer head 1. Therefore, the chemical solution 9 is supplied sufficiently in the vicinity of the edge of the wafer W, while the chemical solution 9 is insufficient in the vicinity of the center of the wafer W.
FIG. 9 is a graph showing the measurement results of polishing rates actually measure data plurality of positions of a processed wafer W. It is understood from this graph that the polishing rate is low at the center zone of the wafer W where the supply amount of the chemical solution 9 is insufficient, and that the polishing rate is high at the edge zone of the wafer W.
Likewise, in the wafer processed according to the first prior art shown in FIG. 6, the polishing rates are not uniform at the center and edge portions of the wafer.
Thus, each of the first and second prior arts is disadvantageous in that the chemical solution cannot be supplied in a satisfactory manner particularly to the wafer center, causing the polishing rates to be uneven at respective parts of the wafer.